Hydrofluorocarbons (“HFCs”) and hydrochlorofluorocarbons (“HCFCs”) are highly desirable for use in a wide range of applications including various solvent, refrigerant, blowing agent, aerosol propellant applications, and the like. Because HFCs and HCFCs tend to exhibit lesser (or no) ozone-depleting characteristics, and tend to be less flammable and less toxic than many chlorine-containing compounds (such as hydrochlorocarbons or chlorofluorocarbons) used conventionally in the aforementioned applications, HFCs and HCFCs have found increasing use as substitutes for conventional chlorine-containing compounds. In light of such increasing use, applicants have recognized a growing need for the efficient and cost-effective production of HFCs and HCFCs.
Many conventional methods of producing HFCs and/or HCFCs involve reacting hydrogen fluoride (“HF”) with one or more chlorinated compounds to produce a reaction product stream comprising the desired HFC or HCFC, as well as, unreacted HF, other starting reagents, and undesirable by-products. For example, WO 95/04022, incorporated herein by reference, describes the synthesis of 1,1,1,3,3-pentafluoropropane (“HFC-245fa,” an HFC further described in U.S. Pat. No. 2,942,036, Canadian Patent No. 684,687, EP 381986A, and JP 2,272,086) including the steps of reacting HF with 1,1,1,3,3,3-hexachlororopropane to produce 1-chloro-1,1,3,3,3-pentafluoropropane and converting such HCFC to HFC-245fa. For any of the methods described above to be relatively efficient and cost-effective, it is desirable that not only the HFC/HCFC product be isolated in good yield and purity, but also that any unreacted HF be isolated and recovered with relatively good purity for recycle and reuse in subsequent reactions. Unfortunately, while some relatively pure HF can be recovered and separated from the product streams of conventional methods using conventional distillation techniques, there is usually a significant portion of HF which cannot be separated, especially where the HF forms an azeotropic or azeotrope-like mixture with the target HFC/HCFC in a product stream. In addition, while conventional aqueous scrubbing techniques can be used to remove HF from an HFC/HCFC product stream to produce purified HFC/HCFC product, such techniques are destructive to the HF which results in less recycle of HF, and thus, less efficiency of the process and higher cost to replace the lost HF.
In an attempt to avoid at least some of the aforementioned problems associated with distillation and aqueous scrubbing, the prior art has suggested a number of methods of separating HF and/or HFC/HCFC products from azeotrope-like mixtures thereof. For example, European patent application EP 472,391 discloses a method of separating 1,1,1,2-tetrafluoroethane (“HFC-134a”) from a mixture containing hydrochlorofluorocarbons using an extraction agent such as trichloroethylene or perchloroethylene, among others. European patent application EP 467,531 discloses a method of separating HFC-134a from a mixture of HFC-134a and HF by passing the mixture through a distillation column to form a residue of pure HFC-134a. U.S. Pat. No. 5,211,817 discloses a process of separating fluorocarbons from azeotropic mixtures with HF by column distillation wherein a vapor sidestream is withdrawn and introducing the sidestream into a rectifying column equipped with a condenser which is operated at a high reflux ratio. U.S. Pat. Nos. 4,944,846, 5,918,481, and 6,328,907 attempt to use pressure swing distillation to achieve separation of azeotropic mixtures of HFCs/HCFCs and HF. Unfortunately, the aforementioned methods are disadvantageous in that they tend to exhibit limited effectiveness in separation and/or are cost prohibitive.
U.S. Pat. No. 5,895,639 (“the '639 patent”), discloses a method of separating hydrogen fluoride from a fluorocarbon/hydrogen fluoride azeotropic mixture using sulfuric acid, particularly concentrated sulfuric acid (about 98 wt. % or greater). While such method may offer some advantages in HF separation over the aforementioned conventional separation methods, nevertheless applicants have achieved certain unexpected and dramatic improvements in HF separation over the methods of the '639 patent. Such unexpected and improved methods are the subject of the present invention.
All of the documents cited hereinabove are incorporated by reference in their entirety.